Vote up?

Related to user styles, I’ve been toying with an idea now for nearly a year. On any new site that supports user profiles or ‘membership’ I have been thinking about adding a utility to allow users to upload their own user style and tie it directly to their profile. In this manner, their style would be applied to the site in any browser, on any machine (no need to have their style installed locally or require any browser extension). Of course this opens up security holes, but as far as I can see, stripping URLs (force data: URIs only) and stripping IE CSS expressions, I don’t see any other drawbacks. Perhaps requiring that any user style pass the W3C CSS validator as well (though that will limit certain techniques such as browser-specific prefixes)?